1. First check the power supply voltage with a multimeter to ensure that the power supply is normal;

2. First test the products one by one, set different device addresses to ensure that the products are normal;

3, 485 requires 2 termination resistors, connected at both ends of the transmission bus, the resistance requirement is equal to the characteristic impedance of the transmission cable. In the short-distance transmission, there is no need to terminate the resistance, that is, the terminal resistance is generally not required below 300 meters;

4, can also solve the problem of insufficient driving ability through 485 hub